Difference Between Forward and Redirect Rules

I have tested some rules, forward and redirect. The only difference I can see is the sending address in the forwarded/redirected email in the final recipients inbox . Both however still retain a copy of the original email in the original recipients inbox. Surely a redirect should do just that and not leave a copy in the original recipients inbox?

This is as intended, most likely to keep a copy for your own administration so to speak.
If you want to remove the copy of this message you can add an extra condition (to your rule) to delete the email.